Pure-silica Zeolites as porous materials have found various commercial uses in the catalysis, adsorption, and ion exchange industries. Beside that, pure-silica zeolites find more and more applications in other areas because of their superior mechanical properties and porosity. In combination with their porous character leading towards a material with a low-dielectric constant, pure-silica zeolites are a strong candidate for a replacement low-dielectric constant (low-k) material for next-generation microprocessors. In order to survive the chemical-mechanical processing steps, the semiconductor industry generally acknowledges a minimum threshold value of 6 GPa (Young's Modulus) for these materials.
Pure silica zeolites have been proposed as low dielectric constant materials for interconnects the first time by Yan et al. (U.S. Pat. No. 6,630,696). The advantage of using pure-silica-zeolites as low-k material is the combination of crystallinity and porosity such that superior mechanical properties and high porosity can be obtained. The final properties can be tuned by using e.g. different crystalline structure (MFI, BEA, MEL . . . ), by tuning the crystalline/amorphous ratio in the synthesis of the films or by adding porogens to the pure-silica zeolite suspension. Typically, pure-silica zeolites have k values below 2.7.
A main showstopper however for the actual use of pure-silica zeolite materials as low-k films in interconnects is their hydrophilicity (contact angle with H2O typically lower than 20 degrees) which is a main issue in low-k dielectrics. The adsorption of moisture within the inner pores of the zeolites can results in a significant increase of the dielectric constant because water has a very high k value (k=80). Hence, it is important to make the zeolites material very hydrophobic to maintain a low-k value.
Post-deposition treatments were proposed in prior art to increase the hydrophobicity of a zeolites film. For example, vapor-phase silylation using chlorotrimethylsilane or hexamethyldisilazane to increase the hydrophobicity of a zeolite film. Since the pore size of silica zeolites is very small, the chlorotrimethylsilane molecules may encounter diffusion limitations and hence difficulties to access the silanol groups inside the zeolites micropores leading to limited increase in hydrophobization.
Dattelbaum et al. (J. Phys. Chem. B, 109 (2005) pp 14551) used a UV treatment to remove the organic template in a zeolites film after depositing said zeolite film, however no organic functionalization and hence no improvement is seen in the hydrophobicity of the zeolite film because only a photochemical decomposition and desorption of the organic material is performed.
Li et al. (Chem. Mater. 2005, 17, 1851-1854) proposes an organic functionalization of the zeolites crystals (and amorphous silica) during the synthesis of the zeolite nanoparticle suspension (prior to spinning). However the final zeolites film obtained after incorporation of said organic molecules to the silica matrix has a lower thermal stability and the increase in hydrophobicity is rather limited.
As a conclusion there is still a need for an efficient method that increases the hydrophobicity of a zeolite film without altering characteristics such as thermal stability and mechanical strength.